Anti-swish mechanism for a damper

ABSTRACT

An anti-swish mechanism for a damper is disclosed to reduce the swish noise heard during movement of a piston assembly within the damper. The damper includes a pressure cylinder which forms a working chamber having a first portion and a second portion operable to store damping fluid. A piston rod is partially disposed within a pressure cylinder and a piston body is secured within the piston rod. Extending from the piston body are first and second annular axially extending lands which are concentric with the piston body. A set of axially extending, circumferentially spaced flow ports are formed in the piston body between the first and second annular axially extending lands. Adjacent to the flow ports is an anti-swish mechanism which reduces &#34;swish&#34; noise as the piston body moves within the pressure cylinder.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to suspension systems for automotive vehicles andmachines which receive mechanical shock, and more particularly to ananti-swish mechanism for a damper.

2. Description of the Related Art

Dampers are used in connection with automotive suspension systems toabsorb unwanted vibrations which occur during driving. To dampenunwanted vibrations, dampers are generally connected between the bodyand the suspension of an automotive vehicle. A piston assembly islocated within the damper and is connected to the body of the automotivevehicle through a piston post which in turn is connected to a pistonrod. Because the piston assembly is able to limit the flow of dampingfluid within the working chamber of the damper when the damper iscompressed or extended, the damper is able to provide a dampening forcewhich "smooths" or "dampens" vibrations transmitted from the suspensionto the body.

As the fluid flows in the damper during compression and rebound strokes,the fluid tends to create an audible "swish" noise which is annoying orunpleasant to the human ear. This swish noise is generally heard duringlow velocity rebound or compression strokes because of the relativelylow noise environment during this period. However, swish noise is alsosometimes heard during higher velocity strokes. This swish noisegenerally occurs as the fluid flows through an orifice which causes aflow restriction prior to the fluid entering a bleed or flow port in thepiston assembly where the flow restriction is reduced (i.e. bleedsection becomes larger or wider). By reducing the flow restriction, alower pressure or under pressure is created (i.e. Bernouilli's equation)at the entrance point or edge of the bleed or flow port which leads tocavitation of the fluid (i.e. forming vapor bubbles) and the resultingswish noise. With conventional piston assembly designs, this point oflow pressure occurs at the entrance edge of the bleed or flow port wherethe fluid enters the bleed or flow port because it is difficult tosupply fluid to this point or edge.

What is needed then is a damper which does not suffer from theabove-mentioned disadvantage. This will, in turn, eliminate or reducethe swish noise associated with conventional dampers during compressionand rebound strokes. It is therefore, an object of the present inventionto provide such an anti-swish mechanism for a damper.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, a damperhaving an anti-swish mechanism is disclosed. The anti-swish mechanism isused to reduce or eliminate swish noise during compression and reboundstrokes of the damper. This is basically achieved by providing ananti-swish mechanism positioned adjacent to flow ports axially extendingthrough a piston assembly of the damper. The anti-swish mechanismreduces swish noise as damping fluid passes through the piston assemblywithin the damper.

In one preferred embodiment, a pressure cylinder forms a working chamberhaving a first portion and a second portion operable to store dampingfluid. A piston rod is partially disposed within the pressure cylinderand a piston body is secured to the piston rod. Extending from thepiston body are first and second annular axially extending lands whichare concentric with the piston body. An annular anti-swish chamber isconcentric with the piston body and positioned between the first andsecond annular axially extending lands. A set of axially extending,circumferentially spaced flow ports are formed concentrically with thepiston body adjacent to the second annular land. As the damping fluidflows from the first portion to the second portion of the workingchamber through the set of flow ports, the damping fluid first passesinto the annular anti-swish chamber to reduce swish noise.

In another preferred embodiment, the damper includes the pressurecylinder which forms the working chamber having the first portion andthe second portion operable to store damping fluid. The piston rod ispartially disposed within the pressure cylinder and the piston body issecured to the piston rod. At least one flow port is formed in thepiston body which allows damping fluid to flow between the first portionand the second portion of the working chamber. A valve disk ispositioned concentrically with the piston body which has a first sideand a second side substantially perpendicular to the piston rod with anouter circumferential edge positioned between the first and secondsides. The outer circumferential edge has a concentrically taperedsurface adjacent to the body such that the concentrically taperedsurface reduces swish noise as the damping fluid passes through a flowport.

Use of the present invention provides a damper which reduces oreliminates swish noise during compression or rebound strokes as thepiston assembly moves within the damper. As a result, the aforementioneddisadvantage associated with the current dampers has been substantiallyeliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

Still other advantages of the present invention will become apparent tothose skilled in the art after reading the following specification andby reference to the following drawings in which:

FIG. 1A is a partial cross-sectional view of a damper incorporating theanti-swish mechanism according to the teachings of one of the preferredembodiments of the present invention;

FIG. 1B is an enlarged cross-sectional view of a piston assembly withinthe damper taken about line 1B in FIG. 1A;

FIG. 2A is an enlarged cross-sectional view of a top portion of thepiston assembly shown in FIG. 1A;

FIG. 2B is an enlarged cross-sectional view of the anti-swish mechanismtaken about line 2B in FIG. 2A;

FIG. 2C is a partial top view of the anti-swish mechanism taken alongline 2C in FIG. 2B;

FIG. 3A is an enlarged cross-sectional view of a top portion of a pistonassembly utilizing another preferred embodiment of the presentinvention;

FIG. 3B is an enlarged cross-sectional view of the anti-swish mechanismtaken about line 3B in FIG. 3A;

FIG. 3C is a partial top view of the anti-swish mechanism taken alongline 3C in FIG. 3B; and

FIG. 4 is an enlarged cross-sectional view of a conventional bleed in apiston assembly without an anti-swish mechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The following description of the, preferred embodiments of the presentinvention are merely exemplary in nature and are in no way intended tolimit the invention or its application or uses. Moreover, while thisinvention is described in connection with an automotive vehicle, thoseskilled in the art would readily recognize that the anti-swish mechanismfor a damper can be utilized with various other devices which requiredampers.

Referring to FIG. 1A, a damper 10 is shown which incorporates onepreferred embodiment of the anti-swish mechanism of the presentinvention. The damper 10 includes an upper end fitting 12 and a lowerend fitting 14 used to secure the damper 10 to an automotive vehicle(not shown). The upper end fitting 12 is connected to an upper capportion 16 of the damper 10 by a weld. The upper end fitting 12 is inturn connected to a body portion of the automotive vehicle. Similarly,the lower end fitting 14 is connected to a lower cap portion 18 so as tosecure the damper 10 to a suspension portion of the automotive vehicle.As will be appreciated by those skilled in the art, other suitable meansmay be used to secure the damper 10 to the automotive vehicle or otherdevices which require a damper 10. It should also be noted that the term"damper" as used herein refers to dampers in a general sense of thephrase and will include MacPherson struts and shock absorbers.

The damper 10 comprises an elongated tubular pressure cylinder 20defining a damping fluid-containing working chamber 22. Disposed withinthe chamber 22 is a reciprocating piston assembly 24. The reciprocatingpiston assembly 24 is used to restrict the flow of damping fluid betweenan upper portion 26 and a lower portion 28 of the working chamber 22 soas to generate damping forces. To provide means for securing thereciprocating piston assembly 24 within the pressure cylinder 20, anaxially extending piston rod 30 and a piston post 32 are provided. Thereciprocating piston assembly 24 is secured to one end of the axiallyextending piston post 32 which is in turn secured to the axiallyextending piston rod 30.

A base valve, generally designated by the numeral 34, is located withinthe lower portion 28 of the pressure cylinder 20 and is used to controlthe flow of damping fluid between the working chamber 22 and an annularfluid reservoir 36. The annular fluid reservoir 36 is defined as thespace between the outer periphery of the pressure cylinder 20 and theinner periphery of a housing 38. The operation of the base valve 34 maybe similar to the operation of the base valve shown in U.S. Pat. No.3,757,910, which is hereby incorporated by reference. However, othertypes of base valves may also be used.

Referring to the reciprocating piston assembly 24, shown best in FIG.1B, the piston assembly 24 comprises a piston body 40 having a pluralityof ridges (not shown) disposed on the annular exterior of the pistonbody 40. The ridges are used to secure an annular TEFLON sleeve 42 whichis disposed between the ridges of the piston body 40 and the pressurecylinder 20. The TEFLON sleeve 42 permits movement of the piston body 40with respect to the pressure cylinder 20 without generating excessfrictional forces.

Upward movement of the piston body 40 is limited by a radially extendedstep portion 44 and a support washer 46. Downward movement of the pistonbody 40 is limited by a threaded nut 48 or similar type fasteningelement which is threadably received upon the piston post 32. A helicalcoil compression spring 50 is arranged concentrically with the supportwasher 46 and bears against an intake valve assembly 52, which will bediscussed in detail shortly. A helical coil rebound spring 54 isarranged concentrically with the nut 48 and is supported at the lowerend by a radially outwardly extending flange 56 on the lower end of thenut 48. The upper end of the rebound spring 54 bears against a springretainer 58 which in turn acts against the underside of a disk shapedvalve member 60 to thereby resiliently urge the valve member 60 intosealing engagement with the piston body 40.

The piston body 40 further includes a first plurality of axiallyextending circumferentially spaced flow ports 62 and a second pluralityof axially extending, circumferentially spaced flow ports 64. The firstplurality of flow ports 62 comprises three circumferentially spaced flowports 62 which are spaced radially outwardly from and concentricallyarranged relative to the second plurality of flow ports 64. The secondplurality of flow ports 64 comprises between two to eightcircumferentially spaced flow ports 64. While the piston body 40contains two pluralities of flow ports 62 and 64, one having threeindividual ports and the other having between two to eight individualports, those skilled in the art would recognize other configurations ofpiston bodies having various numbers of flow ports can be utilized inthe piston assembly 24.

Disposed within an axially downwardly extending counterbore 66 in thepiston body 40 is a lower annular extending land or valve seat 68 spacedradially outward from the second plurality of flow ports 64. The land 68defines a generally radially extending surface which is adapted to beselectively engaged by the upper side of the generally disk shaped valvemember 60. The valve member 60 is adapted to be fixedly retained orsecured to the piston body 40 by being clampingly secured between acombination of the nut 48 and the spring retainer 58 and the combinationof the land 68 and an annular shoulder 70 on the body 40 of the pistonassembly 24. As will be appreciated by those skilled in the art, thatwhile a single valve member 60 is shown, multiple valve members 60 maybe used depending on the damping requirements. As the piston body 40moves upwardly within the working chamber 22 during a high velocityrebound stroke, fluid will flow downwardly through the second pluralityof flow ports 64, thereby forcing the valve member 60 downwardly againstthe resistance of the rebound spring 54, whereby fluid may flow from theupper portion 26 of working chamber 22 to the lower portion 28 of theworking chamber 22.

It should be noted that while the anti-swish mechanisms discussed beloware described in detail with reference to the damper 10 and the pistonassembly 24, the anti-swish mechanisms are not limited to only theconfiguration of the damper 10 and the piston assembly 24 but may beincorporated into numerous other dampers or piston assemblies, both onthe top or bottom of the piston assembly. For instance, the anti-swishmechanisms discussed below could be incorporated into the pistonassembly disclosed in U.S. Pat. No. 4,113,072, which is herebyincorporated by reference.

Turning to FIGS. 2A and 2B, the top portion of the piston assembly 24 isshown which incorporates one preferred embodiment of the anti-swishmechanism of the present invention. The top of the piston body 40includes a first annular axially extending land or valve seat 72 and asecond annular axially extending land or valve seat 74 concentric withthe land 72. The first land 72 and the second land 74 define generallyradially extending surfaces, each of which are on the same planeperpendicular to the piston post 30. These surfaces are selectivelyengaged by a valve member or orifice disk 76 of the intake valveassembly 52. The orifice disk 76 is a generally flat disk shaped valvemember having multiple intake orifices 78 for the second plurality offlow ports 64 which enables the damping fluid to pass between the upperportion 26 to the lower portion 28 of the working chamber 22 during highvelocity rebound strokes. The orifice disk 76 further includes twelveslot orifices 80, show clearly in FIG. 2C, which enables damping fluidto flow through the first plurality of flow ports 62, which will bedescribed in detail shortly. Positioned atop and concentric with theorifice disk 76 is an intake valve member 82 which is also a generallyflat disk shaped valve member. The intake valve 82 includes multipleintake orifices 84, also for the second plurality of flow ports 64. Aswill be appreciated by those skilled in the art, the intake valveassembly 52 includes the two valve members 76 and 82, however, theintake valve assembly 52 can be configured to have addition valvemembers depending on the damping required during the compression stroke,as well as various numbers of intake orifices 78 and 84 or slot orifices80.

Positioned concentrically with and between the first land 72 and thesecond land 74 is an annular axially extending sub-land 86. The sub-land86 axially extends slightly less than the first land 72 and the secondland 74 by about 0.09 mm and has a top radially extending surface ofabout 0.30 mm wide which is about the same surface width as the firstand second lands 72 and 74. Positioned between the first land 72 and thesub-land 86 is an annular anti-swish chamber 88 which is concentric withthe lands 72,74 and 86. The anti-swish chamber 88 has an annular concavesemispherical shape having a width of about 1.0 mm and a depth of about0.6 mm. The edges 90 of the anti-swish chamber 88 have about a 90°entrance angle 91 in contrast to the 120° entrance angles at edges 92 ofthe flow ports 62. While the anti-swish chamber 88 is described above inrelation to specific dimensions, the anti-swish chamber 88 is clearlynot limited to only these dimensions. Moreover, the entrance angle 91 atthe edge 90 is indicated as being about 90°, however, the entrance anglecan also be less than 90°.

In operation, when a low velocity rebound stroke occurs, damping fluidflows from the first portion 26 to the second portion 28 of the workingchamber 22 through the first plurality of flow ports 62. Specifically,the fluid flows from the top portion 26 of the working chamber 22,through the orifices 80 in the orifice disk 76, over the land 72 intothe anti-swish chamber 88, over the sub-land 86 and through the flowports 62. As the fluid follows this path, a high speed fluid flowdesignated by numeral 94 occurs. In addition, the high speed flow 94causes a lower speed secondary fluid flow 96.

As the fluid enters the orifices 80, a flow restriction occurs due tothe restriction caused by the land 72 before the fluid enters theanti-swish chamber 88. Upon entering the anti-swish chamber 88, therestriction is reduced because of the larger area in the anti-swishchamber 88. This causes a slight under pressure at the edge 90 of theland 72. However, because the entrance angle at the edge 90 is about90°, substantially no swish noise is caused. The fluid then passes overthe gap about the circumference between the sub-land 86 and the orificedisk 76 which only causes a slight restriction in the flow of fluid. Thefluid then subsequently flows through the ports 62. Because there isonly a slight restriction of fluid as the fluid enters the ports 62,there is substantially no under pressure at the edge 92 of the sub-land86, which thereby reduces or eliminates swish noise as the fluid passesover the edge 92 and enters the ports 62 during low velocity reboundstrokes. The anti-swish chamber 88 enhances or stimulates fluid rotationin the secondary fluid flow 96 which enables the secondary fluid flow 96to fill the area along the edge 90 of the land 72, thereby reducing theunder pressure (i.e. cavitation) in this area.

As the velocity of the rebound stroke increases, the valve member 60 isresiliently urged against the rebound spring 54 by fluid in the secondplurality of flow ports 64. This creates a second flow path duringrebound consisting of fluid passing into orifices 84 and 78 from theupper portion 26 of the working chamber 22. This fluid passes into theorifices 84 and 78 from around the support washer 46 and through threeaxially extending circumferentially spaced orifices 98 in the washer 46which are concentric with the piston post 30. Conversely, duringcompression, fluid flows from the lower portion 28 of the workingchamber 22, up through the first set of flow ports 62 and resilientlyurges the orifice disk 76 and intake valve 82 upward against the spring50.

Turning to FIGS. 3A-3C, another preferred embodiment of an anti-swishmechanism is shown incorporated into the piston body 40. The piston body40 shown in FIGS. 3A-3C is substantially the same as the piston bodyshown in FIGS. 1A-2C except for the following differences. The firstplurality of flow ports 62 are circumferentially farther out than theflow ports 62 shown in FIGS. 1A-2C. The piston body 40 includes only afirst annular axially extending land or valve seat 99 and a secondannular axially extending land or valve seat 100 concentric with theland 99. The land 100 axially extends slightly less than the first land99 and is selectively engaged by a first valve member or sharp bleeddisk 102. The sharp bleed disk 102 is a generally flat disk shaped valvemember having multiple intake orifices 104 for the second plurality offlow ports 64 which enables the damping fluid to pass between the upperportion 26 to the lower portion 28 of the working chamber 22 during highvelocity rebound strokes. The sharp bleed disk 102 further includes aconcentrically tapered surface adjacent to the piston body 40 at theouter circumferential edge 106 of the sharp bleed disk 102. The angle107 of the tapered edge is less than 90° and preferably between about20° to 40°.

Positioned atop the sharp bleed disk 102 is a second valve member ororifice disk 108. The orifice disk 108 is also a generally flat diskshaped valve member having multiple intake orifices 110 for the firstand second plurality of flow ports 62 and 64 and twelve axiallyextending, circumferentially spaced, elongated slot orifices 112, showclearly in FIG. 3C, which enables damping fluid to flow through thefirst plurality of flow ports 62, which will be described in detailshortly. Positioned atop and concentric with the orifice disk 108 is anintake valve member 114 which is also a generally flat disk shaped valvemember. The intake valve 114 includes multiple intake orifices 116, alsofor the first and second plurality of flow ports 62 and 64.

In operation, when a low velocity rebound stroke occurs, damping fluidflows from the first portion 26 to the second portion 28 of the workingchamber 22 through the first plurality of flow ports 62. Specifically,the fluid flows from the top portion 26 of the working chamber 22,through the multiple intake orifices 116 and 110, into the elongatedslot orifices 112 and through the flow ports 62. As the fluid followsthis path, a high speed fluid flow designated by numeral 118 occurs. Inaddition, the high speed flow 118 causes a lower speed secondaryrotating fluid flow 120. The concentrically taper surface of thecircumferential edge 106 reduces restriction of the fluid and enablesthe secondary fluid flow 120 to fill the area immediately along the edge106 of the sharp disk 102, thereby reducing the under pressure (i.e.cavitation) in this area to reduce or eliminate the swish noise duringlow velocity rebound strokes.

Similar to the embodiment in FIGS. 1A-2C, as the velocity of the reboundstroke increases, the valve member 60 is resiliently urged against therebound spring 54 by fluid in the second plurality of flow ports 64.This creates a second flow path during rebound consisting of fluidpassing into intake orifices 104, 110 and 116 from the upper portion 26of the working chamber 22. This fluid passes into the intake passages104, 110 and 116 from around the support washer 46 and through the threeaxially extending orifices 98 in the washer 46. Conversely, duringcompression, fluid flows from the lower portion 28 of the workingchamber 22, up through the first plurality of flow ports 62 andresiliently urges the sharp disk 102, orifice disk 108 and intake valve114 upward against the spring 50.

Turning now to FIG. 4, a conventional piston assembly 24 is shown whichdoes not incorporate the above-identified anti-swish mechanisms. Thepiston body 40 in FIG. 4 is similar to that shown in FIGS. 3A-3C andincludes the first and second plurality of flow ports 62 and 64 and thefirst and second lands 99 and 100. The lands 99 and 100 in FIG. 4 are onthe same plane perpendicular to the piston post 30 with the orifice disk76 and intake valve 82, as shown in FIGS. 1A-2C, positioned atop thelands 99 and 100. The orifice disk 76 includes the intake orifices 78and slot orifices 80 and the intake disk 82 includes the intake orifices84. The first plurality of flow ports 62 are also positionedcircumferentially out from the first plurality of flow ports 62 shown inFIGS. 1A-2C, similar to that shown in FIGS. 3A-3C.

During a low velocity rebound stroke, damping fluid flows from the firstportion 26 to the second portion 28 of the working chamber 22 throughthe first plurality of flow ports 62. Specifically, the fluid flows fromthe top portion 26 of the working chamber 22, through the orifices 80 inthe orifice disk 76, over the land 99 and through the flow ports 62. Asthe fluid follows this path, a high speed fluid flow designated bynumeral 122 occurs. In addition, the high speed flow 122 causes a lowerspeed secondary rotating fluid flow 124. As the fluid enters theorifices 80, the flow is restricted due to the land 99. Because of thisand the large entrance angle 125 (i.e. 120 degrees) at edge 126, thefluid flowing from the restricted slots 80 into the larger ports 62causes an under pressure along the edge 126. This under pressureinhibits the secondary oil flow 124 from reaching this area and causesthe fluid to vaporize or create bubbles 128 which are heard as the swishnoise during the low velocity rebound stroke. Such a condition isreduced or eliminated in the above-identified embodiments since the flowrestriction prior to entering the ports 62 is reduced, as well as makingthe entrance angle of the edge over which the flow restriction enters alarge area 90° or less. For example, comparing the swish noise of theembodiment shown in FIGS. 1A-2C with that shown in FIG. 4, the damper inFIG. 4 creates 56 dB (0-16 kHz) of swish noise compared to 50 dB (0-16kHz) for the damper 10 in FIGS. 1A-2C.

It should also be noted that the embodiment in FIGS. 1A-2C allows moredesign freedom with respect to placement of the ports 62 in relation tothe orifice slots 80 because of the use of the anti-swish chamber 88. Inthe embodiment in FIGS. 1A-2C, the sub-land 86 will act as an obstaclethat divides the fluid over the whole circumference of the anti-swishchamber 88. In other words, all the fluid which enters the orfice slots80 first passes through the anti-swish chamber 88. In contrast, thedamper shown in FIG. 4 shows the ports 62 positioned in line (i.e. 0degrees) with the orifice slots 80. If the orifice slots 80 are turnedor rotated 90° from the ports 62, the fluid flows into the orifice slots80 and through a groove for a quarter circle before it enters the ports62 which effects damping and the amount of swish noise heard. Thus, byuse of the sub-land 86 and anti-swish chamber 88, positioning of theorfice slots 80 about the circumference of the orfice disk 76 is not ascritical as is the damper shown in FIG. 4.

As appreciated by those skilled in the art, while the above anti-swishmechanisms are discussed in detail in relation to low velocity reboundstrokes, the anti-swish mechanisms could also be used for both therebound or compression strokes and for either high or low velocitystrokes. This would be achieved by merely positioning the anti-swishmechanisms adjacent to the flow ports where swish noise is occurring.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. One skilled in the art willreadily recognize from such discussion, and from the accompanyingdrawings and claims, that various changes, modifications and variationscan be made therein without departing from the spirit and scope of theinvention as defined by the following claims.

What is claimed is:
 1. A damper comprising:a pressure cylinder forming aworking chamber operable to store damping fluid; a piston rod at leastpartially disposed within said pressure cylinder; a piston body disposedin said pressure cylinder and secured to said piston rod, said pistonbody separating said working chamber into a first portion and a secondportion; a continuously open flow path extending between said first andsaid second portions of said working chamber; a first annular axiallyextending land being concentric with said piston body; a second annularaxially extending land being concentric with said piston body; aplurality of axially extending, circumferentially spaced flow portsformed concentrically with said piston body between said first annularaxially extending land and said second annular axially extending land;and anti-swish means positioned adjacent to said circumferentiallyspaced flow ports for reducing swish noise as said piston body moves insaid pressure cylinder, said anti-swish means being disposed within saidopen flow path and including an annular axially extending sub-land beingconcentric with said piston body and positioned between said firstannular axially extending land and said second annular axially extendingland.
 2. The damper as defined in claim 1 wherein said sub-land ispositioned adjacent to said plurality of axially extending,circumferentially spaced flow ports.
 3. The damper as defined in claim 2wherein said anti-swish means further includes an annular anti-swishchamber being concentric with said piston body and positioned betweensaid first annular axially extending land and said annular axiallyextending sub-land.
 4. The damper as defined in claim 3 wherein saidannular axially extending sub-land axially extends less than said firstannular axially extending land, whereby as said damping fluid flows oversaid annular axially extending sub-land, said sub-land creating less ofa fluid restriction as said damping fluid flowing over said firstannular axially extending land.
 5. The damper as defined in claim 4wherein said annular anti-swish chamber has a concave semisphericalshape with a first edge adjacent said first annular axially extendingland and a second edge adjacent to said annular axially extendingsub-land, said first and second edges having an entrance angle of about90° or less.
 6. The damper as defined in claim 5 wherein during a strokeof said piston body, damping fluid flows over said first annular axiallyextending land, into said anti-swish chamber, over said annular axiallyextending sub-land and into said plurality of axially extending,circumferentially spaced flow ports, said fluid flow generating a firsthigh speed fluid flow and a second lower speed fluid flow, saidanti-swish chamber stimulating rotation of said second fluid flow,whereby fluid flows along an edge of said first annular axiallyextending land to reduce under pressure along said edge for reducingswish noise as said piston body moves in said pressure cylinder.
 7. Adamper comprising:a pressure cylinder forming a working chamber operableto store damping fluid; a piston rod at least partially disposed withinsaid pressure cylinder; a piston body disposed in said pressure cylinderand secured to said piston rod, said piston body separating said workingchamber into a first portion and a second portion; a continuously openflow path extending between said first and said second portions of saidworking chamber; a first annular axially extending land being concentricwith said piston body; a second annular axially extending land beingconcentric with said piston body; an annular axially extending sub-landbeing concentric with said piston body and positioned between said firstannular axially extending land and said second annular axially extendingland an annular anti-swish chamber being concentric with said pistonbody between said first annular axially extending land and said secondannular axially extending land, said anti-swish chamber being disposedwithin said open flow path; and a plurality of axially extending,circumferentially spaced flow ports formed concentrically with saidpiston body adjacent to said second annular land, wherein said dampingfluid flows from said first portion to said second portion of saidworking chamber through said plurality of axially extending,circumferentially spaced flow ports, with said damping fluid firstpassing into said annular anti-swish chamber to reduce swish noise. 8.The damper as defined in claim 7 wherein said sub-land is positionedadjacent to said set of axially extending, circumferentially spaced flowports.
 9. The damper as defined in claim 8 wherein said annular axiallyextending sub-land axially extends less than said first annular axiallyextending land, whereby as said damping fluid flows over said annularaxially extending sub-land, said sub-land creates less of a fluidrestriction as said damping fluid flows over said first annular axiallyextending land.
 10. The damper as defined in claim 9 wherein saidannular anti-swish chamber has a concave semispherical shape with afirst edge adjacent said first annular axially extending land and asecond edge adjacent to said annular axially extending sub-land, saidfirst and second edges having an entrance angle of about 90° or less.